If prosecutors in Poland and Germany decide not to charge alleged Nazi commander Michael Karkoc with war crimes, it's likely he would live out the rest of his life in the United States.

While U.S. officials have successfully stripped more than 100 Nazi collaborators of their citizenship, the government has found it difficult to deport them.

An Associated Press investigation concluded that the 94-year-old Karkoc, who lives in Minneapolis, was a founder and an officer in the SS-led Ukrainian Self Defense Legion.

His family has denied the allegations, in spite of a Ukrainian-language memoir Karkoc published in 1995 detailing his membership in the military unit.

The AP investigation showed Karkoc lied about his military service when he entered the United States in 1949. That would give the government legal grounds to revoke Karkoc's citizenship, but the process, known as denaturalization, is time-consuming.

As with any federal lawsuit, a denaturalization case is subject to appeal all the way to the U.S. Supreme Court. Once denaturalization is complete, a deportation order must be issued through a separate legal process.

Deportation orders also can be appealed. It typically takes a minimum of six years to exhaust all those appeals.

Even if Karkoc lived to be 100, it's still not certain he could be removed from the United States.

"The U.S. can't deport someone unless there's a country willing to accept that person," said Stephen Paskey, who spent seven years prosecuting Nazi collaborators as a senior trial attorney for the U.S. Department of Justice. "What has happened with many of these guys is that they are stateless after their U.S. citizenship has been revoked.... And so there is no country that is obligated to take them, and there's no country that is willing to take them."

Vladas ZajanckauskasAP Photo/U.S. Department of Justice

There are at least four Nazi collaborators who have been stripped of their citizenship, ordered deported, exhausted their appeals and are still living in the United States.

Among them is Vladas Zajanckauskas, a member of a battalion assigned to "liquidate" Jews in a Warsaw ghetto in 1943. After the U.S. government discovered Zajanckauskas living in Massachusetts, he was denaturalized in 2005 and ordered deported in 2007.

Now 97, he has yet to be removed.

"[Zajanckauskas'] victims surely did not see justice done in 1943," said Eli Rosenbaum, director of strategy and policy for the Justice Department division charged with prosecuting Nazis living in the United States. "And if no European government fulfills its moral obligation to take him back -- and soon -- then justice won't be done now either."

Rosenbaum made the remarks in a speech this April at the U.S. Holocaust Memorial Museum. The Justice Department declined an interview request.

People who have been ordered deported but have no country to take them are free to go about their lives in the United States, Paskey said, although they lose the benefits of citizenship, including Social Security payments.

The last Nazi collaborator deported by U.S. was John Demjanjuk, in 2009. The former Cleveland auto worker died last year in Germany, while appealing his conviction for war crimes. He was 91.

Paskey said the best chance of removing Karkoc from the United States would be for either Poland or Germany to indict him on war crimes. That's more likely to happen in his case than with other alleged Nazis discovered in the last decade, because Karkoc's memoir identifies him as a commander.

"The rules for commanders are different under war crimes law," Paskey said. "He did not simply follow orders. He issued orders."

But Paskey said it's not a slam dunk, either. With the exception of Demjanjuk, Germany has been reluctant to prosecute Nazis from other countries. Poland, he said, hasn't pursued a war crimes case in the last decade.